ST Elevation Myocardial Infarction (STEMI)

I21.0-I21.4/I21.9/I22.0-1/I22.8-9

• Description
• Medicine treatment
• Referral

DESCRIPTION

Ischaemic chest pain that is prolonged, or associated with nausea, sweating and syncope or associated with persistent ST elevation or new or presumed new left bundle branch block (LBBB). Repeat ECG at 20-30 minute intervals if the initial ECG is not diagnostic.

MEDICINE TREATMENT

• Oxygen if saturation <94%.

LoEI [7]

• Clopidogrel, oral, 75 mg daily for one month.

LoEI [8]

AND

• Aspirin, oral, 150 mg immediately as a single dose (chewed or dissolved).
  • Followed with 150 mg daily (continued indefinitely in absence of contraindications).

LoEI [9]

AND

Thrombolytic therapy

• Streptokinase, IV 1.5 million units diluted in 100 mL sodium chloride 0.9%, infused over 30–60 minutes. Do not use heparin if streptokinase is given.
  • Hypotension may occur. If it does, reduce the rate of infusion but strive to complete it in <60 minutes.
  • Streptokinase is antigenic and should not be re-administered in the period of 5 days to 2 years after 1st administration.
  • Severe allergic reactions are uncommon but antibodies which may render it ineffective may persist for years.

LoEI [10]

OR

If streptokinase is unavailable:

• Alteplase, IV infusion:
  • Do not exceed 100 mg.
  • if history of onset is less than 6 hours (beyond 6 hours consult a specialist or treat as NSTEMI (see below):

LoEI [11]

• Indications and contraindications are similar to those for streptokinase as above (except that prior use of streptokinase is not a contraindication).

Monitor the following, continuously and also during transfer:

• pulse
• BP
• respiration depth and rate (count for a full minute)
• ECG

Note: Defibrillator should be readily available at all times including during transport.

Adjunctive treatment

• Enoxaparin (after alteplase, do not use heparins after streptokinase).
  • Loading dose: IV, 30 mg as a bolus, followed by SC, 1 mg/kg as a single dose (total cumulative dose not to exceed 100 mg).
  • Maintenance dose: SC, 1.5 mg/kg daily or 1 mg/kg 12 hourly.

LoEI [12]

In the elderly (>75 years of age), omit IV loading dose and reduce SC dose:

• Loading dose: SC, 0.75 mg/kg as a single dose.
• Maintenance dose: SC, 1.5 mg/kg daily or 1 mg/kg 12 hourly.

LoEI [13]

Pain not responsive to thrombolytics may suggest ongoing unresolved ischaemia.

LoEI [14]

• Nitrates, e.g.:
• Isosorbide dinitrate, SL, 5 mg immediately as a single dose.
  • May be repeated at 5-minute intervals for 3 or 4 doses.

For ongoing chest pain, to control hypertension or treat pulmonary oedema:

• Glyceryl trinitrate, IV, 5–200 mcg/minute, titrated to response.
  • Start with 5 mcg/minute and increase by 5 mcg/minute every 5 minutes until response or until the rate is 20 mcg/minute.
  • No response after 20 mcg/minute, increase by 20 mcg/minute every 5 minutes until a pain response or medicine is no longer tolerated.
  • Flush the PVC tube before administering the medicine to patient.
  • Monitor BP carefully.

Dilution of Glyceryl trinitrate:

For severe pain unresponsive to nitrates:

• Morphine, IV, to a total maximum dose of 10 mg (See MORPHINE, IV, for individual dosing and monitoring for response and toxicity).
  • Ongoing severe pain despite all appropriate treatment above is an indication for urgent referral.

When clinically stable without signs of heart failure, hypotension, bradydysrhythmias or history of asthma:

• Cardio-selective ß-blocker, e.g.:
  • Atenolol, oral, 50 mg daily.
• HMGCoA reductase inhibitors (statins), e.g.:
  • Simvastatin, oral, 40 mg at night.

LoEI [15]

Patients on protease inhibitor:

• Atorvastatin, oral, 10 mg at night.

LoEI [16]

Patients on amlodipine (and not on a protease inhibitor):

• Simvastatin, oral, 10 mg at night.

LoEI [17]

If patient complains of muscle pain:

Reduce dose:

• HMGCoA reductase inhibitors (statins), e.g.:
  • Simvastatin, oral, 10–20 mg at night.

OR

Consult specialist for further management.

LoEI [18]

For LV dysfunction following myocardial infarction, heart failure or ejection fraction < 40%:

• ACE-inhibitor, e.g.:
• Enalapril, oral, target dose, 10 mg 12 hourly.
  • Institute other therapy for heart failure and LV dysfunction as described below – see: Congestive cardiac failure.

If ACE-inhibitor intolerant, i.e. intractable cough:

• Angiotensin receptor blocker (ARB), e.g.:
  • Losartan, oral, 50–100 mg daily. Specialist initiated.

• Angioedema is a potentially serious complication of ACE-inhibitor/ angiotensin receptor blocker treatment and if it occurs stop the medication and do not re-challenge.
• Concomitant use of fluoroquinolones with ACE-inhibitor/angiotensin receptor blocker is contraindicated in moderate to severe renal impairment (CrCl ≤30 mL/minute) and in the elderly. Assess renal function before initiating treatment and monitor during treatment.

LoEI [19]

REFERRAL

• Refractory cardiogenic shock.
• Refractory pulmonary oedema.
• Haemodynamically compromising ventricular dysrhythmia.
• Patients with the combination of new right bundle and posterior fascicular block post MI should be referred for permanent pacemaker consideration as they are at high risk for progression to complete heart block.
• Myocardial infarction-related mitral regurgitation or ventricular septal defect (VSD).
• Contraindication to thrombolytic therapy provided PCI facility available (confirm with cardiologist).
• Ongoing ischaemic chest pain.
• Failed reperfusion (<50% reduction in ST elevation at 90 minutes in leads showing greatest ST elevation, especially in anterior infarct or inferior infarct with right ventricular involvement).